With increasing high integration, high speed and high performance of semiconductor devices in the field of electronic materials in recent years, the delay times caused by greater interconnect resistance and greater electric capacity of semiconductor integrated circuits are becoming more serious problems. In order to mitigate the delay times and increase semiconductor device speeds, it has become necessary to use low-permittivity insulating films in circuits.
Various attempts have been made to create porosity in materials in order to achieve even lower permittivity for insulating films. The methods for creating porosity include a method in which thermal decomposing components (porogens) are mixed or bonded therewith, and the porogens are decomposed during the heated firing step for formation of the insulating film, to form pores in the insulating film. However, the sizes of the pores present in films that are rendered porous by such methods are relatively large, being between several nanometers and several tens of nanometers, and because the pores are not independent but interconnected, the strength of the material is necessarily reduced, while several problems also arise as a result of the pores during the semiconductor process. Although introduction of processes such as pore sealing has been studied as a way of solving these problems, this can potentially increase the number of steps and the cost for production.
For example, as disclosed in Japanese Unexamined Patent Publication No. 2001-332543, materials are known that have numerous pores on the molecular level inside a resin structure. According to this prior art, pores are formed on the molecular level by bonding between a first crosslinking component and second crosslinking component, thus lowering the permittivity. However, such materials have been extremely difficult to manage, because they tend to undergo gelling during synthesis of the resins, and the solubility of the polymers during synthesis and their storage life as varnishes are poor.
Materials comprising compounds with —C≡CH bonds in the molecule are disclosed in Japanese Unexamined Patent Publication No. 2005-41938, for example. Because such materials require increased crosslink density in order to obtain sufficient mechanical strength, —C≡H groups are left in the molecule at above a fixed proportion. However, resin films composed of such materials have not exhibited satisfactory permittivity.